The Rodney King incident impressed upon us the importance of video evidence for unraveling what really happened at traffic stops. Between then and now, literally every police cruiser has a dash-cam - but this only provides a narrow view of the entire citizen encounter.
The national news media have documented the mistakes of judgment that police officers have made which have lead to hundreds of lives lost. The dash cam videos are occasionally very insightful, e.g., Sandra Bland's death, some very central police-encounters have 0 footage, e.g., Michael Brown's death, and some police-citizen encounters are not documented by police, but by citizens, e.g., Freddie Gray.
The media does it for profit. The cops should have body cameras to regain their good name and honor, and citizens' safety.